Generally, in a process for forming an LDI (LCD Drive IC), a gate is formed, and a layer having an ONO (Oxide, Nitride, Oxide) structure is formed on the gate. Thereafter, the ONO layer is then selectively etched by performing patterning, and a cleaning process is performed.
However, according to a prior art as set forth above, membranes of the ONO layer are separated during the process of etching the ONO layer; and thus, it causes a problem to produce undesired polymers. Hereinafter, problems induced in a method for fabricating a semiconductor device according to the prior art will be schematically described with reference to drawings.
FIG. 1A to FIG. 1F are process cross-sectional views illustrating a method for manufacturing a semiconductor device according to the prior art. First, as shown in FIG. 1A, a gate 4 is formed on a semiconductor substrate 2; and, as shown in FIG. 1B, a first oxide layer 6, a nitride layer 8 and a second oxide layer 10 are sequentially formed on the semiconductor substrate 2 including the gate 4.
Thereafter, as shown in FIG. 1C, a first photoresist layer pattern 12 is formed on the second oxide layer 10 for patterning the second oxide layer 10. As shown in FIG. 1D, the second oxide layer 10 is selectively etched through a dry etching process by using the first photoresist pattern 12 as a mask. In addition the first photoresist layer pattern 12 is removed. During the etching process, a first polymer 14 is generated on the nitride layer 8 at both sides of the second oxide layer 12.
Because an etching process, e.g., a drying etching, is applied to the nitride layer 8 without removing the first polymer 14, the first polymer 14 serves as an additional mask. That is, as shown in FIG. 1E, the nitride layer 8 is selectively etched by using both the first polymer 14 and the second oxide layer 10a as masks. At this time, since the nitride layer 8 is also etched by using a dry etching process, a second polymer 15 is additionally generated on the first oxide layer 6 at both sides of the nitride layer 8, similarly to the etching process of the second oxide layer 10.
And, since the etching process of the first oxide layer 6 is also, in the prior art, applied without removing the second polymer 15, as shown in FIG. 1F, the first oxide layer 6 is selectively etched by using both the second polymer 15 and the nitride layer 8a as masks. During this time, because the first oxide layer 6 is etched by using a wet etching process, polymers are not generated at both sides of the first oxide layer 6.
Polymers 14 and 15 generated through such processes are separated and lifted from the second oxide layer 10a and the nitride layer 8a during the following heating process. In FIG. 2, photographs of such lifted polymers are shown. The lifted polymers adhere to a device such as a chamber and therefore cause semiconductor equipment to be contaminated thereby.
Accordingly, it is difficult to secure a margin between the ONO layer and the gate since a critical dimension (CD) is hard to control due to the polymers generated during the etching process of the ONO layer. Furthermore, there occurs a contamination of the semiconductor equipment due to the lifted polymers.